Effusion cell and method for use in molecular beam deposition

An effusion cell comprising:

• a crucible having lateral and end walls that form a cavity;
• said cavity having a longitudinal axis, a closed end and an open end;
• said lateral wall having a base longitudinal region adjacent said closed end, a tip longitudinal region adjacent said open end, and a central longitudinal region between said base and tip regions;
• first heater filaments extending substantially along said axis and being located laterally adjacent said tip region;
• second heater filaments extending substantially along said axis and being located laterally adjacent said central region;
• and
• third heater filaments extending substantially along said axis and being located laterally adjacent all of said regions;
• wherein the radial density of the number of said heater filaments is lower adjacent said base region than adjacent said tip or central regions;
• a multiplicity of boron nitride annular spacers located around said lateral wall and distributed along said longitudinal axis;
• each of said spacers having a first, second and third ring of holes, said first ring being located closest to said axis, said third ring being located farthest from said axis, and said second ring being located between said first and second rings;
• wherein said first filaments pass through the holes of said first ring in a first subset of said spacers, said second filaments pass through the holes of said first ring in a second subset of said spacers, and said third filaments pass through the holes of said second ring;
• wherein the holes of said first and second rings have azimuthal angles that are offset with respect to one another;
• wherein the holes in each of said first and second rings are periodically spaced around the circumference of said ring, and wherein said offset corresponds approximately to one-half the pitch of said periodic spacing;
• wherein in each of said first and second rings the arrangement of said holes and the diameter of said filaments are designed so that the spacing of said filaments is approximately equal to the diameter of said filaments;
• a tantalum foil enclosure that blocks gaseous nitrogen, said filaments and said spacers being located within said enclosure,
• a temperature sensor located adjacent said base region and a temperature sensor located adjacent said tip region, and wires coupled to said sensors passing through the holes of said third ring.

An effusion cell comprising:

• a crucible having lateral and end walls that form a cavity;
• said cavity having a longitudinal axis;
• at least one heater filament extending substantially along said axis and being located adjacent said lateral wall;
• a multiplicity of dielectric annular spacers located around said lateral wall and distributed along said longitudinal axis;
• said spacers having a multiplicity of holes through which said at least one filament passes;
• and
• a gas-blocking enclosure, said at least one filament and said spacers being located within said enclosure.

An effusion cell comprising:

• a crucible for containing source material, said crucible having an open end;
• at least one heater filament for healing said source material to evaporation from said open end;
• a multiplicity of dielectric spacers for supporting said at least one filament, said spacers emitting gas when heated;
• and
• an enclosure in which said at least one filament and said spacers are located, said enclosure being configured to block egress of said gas from the region thereof proximate said open end of said crucible.